Process for coloring an anodized aluminum sheet



United States Patent 3,218,243 PROCESS FOR COLORING AN ANODIZED ALUMINUM SHEET Christian E. Michelson, Hamden, (301111., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Filed Oct. 31, 1961, Ser. No. 148,823

4 Claims. (Cl. 204-35) This invention relates to forming arrays of colored areas on metal oxide coated sheet material. More particularly, it relates to imparting coloring substances to anodized coatings on aluminum.

Numerous processes have been developed for the coloring of anodized coatings on the surface of metals containing aluminum. In a few of these processes the coloring is imparted to the surface as the anodizing process is carried out. In others, coloring agents are applied to the anodized surfaces and some treatment is employed to make the added color fast, i.e., to prevent removal by common leaching agents and in normal handling and use.

A number of problems have persisted in the art of coloring anodized aluminum among which are the followmg:

A highly desirable advantage in processes for the surface coloring of aluminum alloys is the development of intense color in the anodized surface in a short time interval.

Another advantage which has been sought after is the development of intense colors from a wide variety of dyes and other coloring agents of such agents are applied, i.e., the multicoloring of an anodized aluminum to impart an array of intensely colored areas thereto.

Still another important desirable attribute of multicoloring processes is an economy in the use of materials or steps to be carried out in producing multicolored patterns having intense coloration.

A problem which has also attended the formation of multicolored patterns with intense colors is that of providing sharply defined edges or limits to the colored areas particularly for contiguous areas which are intensely colored with different colors.

One object of this invention is to provide a method which makes possible formation of multicolored surfaces having the attributes and advantages described above.

Another object of the invention is to provide a method of applying arrays of multicolored areas of sharp definition to anodized surfaces to extend the uses which may be made of articles so decorated.

Other objects and advantages of the method will be in part apparent and in part pointed out in the description which follows.

In one of its broader aspects the objects of the inven tion may be carried out by disposing in contact with an anodized surface a layer of a vehicle in a defined area, said vehicle being subject to thinning with water and containing a colored dye substance, forming over said disposed layer an adherent layer of a coating material permeable to moisture but resistant to being thinned by water.

Vehicles which are subject to being thinned by water, or which may be dispersed temporarily or permanently in water, and which are useful in practice of the present method include many common materials having a base which renders them susceptible to being used in a thickened or paste like consistency. Base materials such as gelatin, glue, and other proteinaceous materials as well as pastes formed from casein, starches, polyvinyl alcohol, gum tragacanth, and other similar materials are useful.

The consistency of the material which can be thinned by water is selected based on a number of factors including the nature of the dye or other coloring substances 3,218,243 Patented Nov. 16, 1965 to be included in the vehicle, the manner in which it is to be applied to the anodized surface, the type of drying or other treatment to be given to the disposed layer, and the nature of the protective overcoating to be applied to the disposed layer, as well as the manner of application of this overcoating. For example, where the layer is to be applied by spraying of the water-thinned vehicle, a greater extent of thinning with water is usually employed than when the vehicle is applied by a brush. Further, a slightly different consistency is preferred where the vehicle is applied through silk screening. Similarly, where it is desired to obtain a wash effect, a vehicle of relatively thin consistency is applied as by brushing within certain areas, and this applied layer is permitted to dry. The dried layer may then be overcoated with layers of water-thinned vehicle of higher concentration and thicker consistency where sharper definition of the edges of these areas is desired.

Generally, any coloring agent, compatible with a vehicle subject to being thinned by water, can be included in the layer disposed in contact with the anodized aluminum sheet, where the agent is in high concentration and has the capability of releasing intense coloration to the anodized metal surface. For example, particles of dye material normally soluble in organic solvents or in oil media may be dispersed in a vehicle, such as a starch paste subject to being thinner by water, and may be disposed, pursuant to this invention, on the anodized aluminum surface in preparation for the permanent transfer of color to said surface.

One of the distinct features of this invention is in the development of intensely colored multicolored arrays on an anodized surface by use of high concentration of coloring agent directly in contact with the anodized surface. The use of thin layers of paste like materials and the drying of these materials into even thinner layers brings high concentrations of coloring agent into contact with the anodized surface layer to be colored.

The concentration of coloring agent and the intensity of color which can be developed from the deposited layers is higher than has been attainable heretofore in multicolored anodized elements. One essential reason for this is that it has been discovered, contrary to expectations, that a high concentration of a water soluble dye can be applied to an anodized surface and sealed in the surface with very sharp clear definitions of edges of the colored zones even though the sealing operation involves immersion of the article and deposited water soluble dye in boiling water. This result is brought about unexpectedly because of the unusual effectiveness discovered for polymeric overlayers which are deposited over the areas bearing the dyes. The overlayers used must be insoluble in water but permeable to moisture.

Moreover, it has been found that dyes and other pigmenting agents which are soluble in Water, or are readily dispersed or thinned by water, in essentially the same manner as the water-thinned vehicle itself, are most useful in practicing this invention because of the greater facility of manipulation made possible; because of the sharp definition of the edges of colored areas; because of the great intensity of the color which can be developed in the anodized surface layer; and because the cost of the coloring process is reduced where this combination of advantages is present. Examples of water soluble dyes which have been found particularly useful in carrying out this invention include: Sandoz Aluminum Series such as Gold S, Copper BF, Red B, Orange 2B, and Yellow A, as well as the greens, blues, violets, etc., of the series; Durand and Huguenin Aluminum Series such as Yellow GL, Red RLW as Well as the blues, violets, blacks, etc., of the series; Ciba Oxanol Aluminum Colors. In addition, many dyes contained in concentrated form in a variety of colored pencils and other marking devices available in art supplies, hobby kits, and other sources have proven satisfactory.

Whether the coloring agent is thinned by water or by organic solvents or oil, the sole characteristic required for use in this method is that it can be applied in concentrated form directly to the anodized surface film and can impart intense coloration to this film.

A distinct advantage of the present method lies in the compatibility of the nature of the dyes applied to the anodized sheet with the character of the anodized surface layer itself. It has been discovered that hydration of the aluminum oxide of the anodized layer is responsible for a sealing action which takes place when anodized aluminum is immersed in boiling water. However, it has also been found that although vehicles subject to being thinned by water serve as exceptionally good carrying media for imparting coloring agents to anodized aluminum where an attempt is made to seal the aluminum oxide surface layer by the use of boiling water or steam, a bleeding of the coloring agents takes place which cancels a number of the advantages which can be obtained through use of water-thinned vehicles and coloring agents. It has now been discovered that the important advantages made available through the use of water-thinned vehicles and coloring agents can be retained in carrying out the multicoloring of the anodized layer where the disposed layer of vehicle contains the coloring agent in high concentration, where the layer is first brought to a relatively dry state, and where the deposited coloring agent is then overcoated with a protective coating which is resistant to solution with, or thinning by water, but which is permeable to moisture. Numerous compositions can be employed in forming the protective overcoatings, or these coatings can be of the preformed type which are applicable in film form directly to the disposed layer.

Surprisingly, it has been found that water soluble dyes, which would ordinarily be completely removed from an anodized oxide layer by a sealing operation, is essentially completely retained in sharply defined colored pattern when first coated with a water insoluble but water permeable polymeric overcoating.

It is essential that the protective coating remain in. intimate contact with the disposed layer during the sealing operation. The selection of protective coatings can be made from the wide variety which are available based on meetingthese three criteria, namely, it must have at least a limited permeability to liquid or vaporous water; it must resist solution or thinning when contacted by steam or boiling water; and it must remain in contact with the surface to be protected until the coloring agent has become sufificiently fixed in the anodized layer that excessive bleeding does not occur.

Suitable protective coating can be formed from lacquer compositions such as acrylic, nitrocellulosic or similar resins dissolved in organic solvents such as methyl ethyl ketone, tetrahydrofurfurol, alcohols, esters, and the like. These lacquers are applied to the surface on which the color bearing layer is disposed. Alternatively, a preformed protective coating permeable to water but resistant to removal by water may be applied to the surface and retained in contact therewith by adhesive action or other retaining means. Coatings found suitable for protecting a deposited layer containing a high concentration of coloring agent are disclosed in US. Patent No. 2,462,029, and other patents.

Suitable protective coatings include those formed with .vinyl, acrylic, or acetate bases as from lacquers which may be thinned with an appropriate organic solvent and applied over the deposited layer. When lacquers are employed, it is necessary only that a protective overlayer remains, after solvent evaporation, for a time to prevent excessive leaching or movement of the dye upon immersion of the dyed article in boiling water. Vehicles of the class forming removable or strippable films, as typi fied by polyvinyl base films, are also convenient protectective coatings as are coatings formed from organic solvent soluble adhesives or cements and asphalts.

Where the protective coating is formed from a lacquer or other non-aqueous liquid composition, it is first permitted to dry to provide an integrated coating in contact with the layer disposed on the anodized surface. One of the more surprising discoveries resulting from the studies of these methods is that a single water permeable insoluble polymeric coating is effective in protecting several deposited proximate layers of concentrated coloring agents although the polymeric coating is not itself part of the deposited layer of coloring agent.

The sealing operation is conveniently carried out by immersing the protected article in boiling water for about ten minutes. Longer times may be required for thicker coatings.

After the sealing is completed, remaining surface layers or coatings such as the protective overcoating, waterthinned media, excess surface colorants, etc., are removed with solvents or by other convenient means to leave the multicolored anodized layer intact. Protective coatings which resist the action of water for a time (sufficient to permit the dye to become fixed to the internal surfaces), but which are removed after the sealing is essentially complete, in the sense of hydration reactions occurring between the oxide of the anodized layer and boiling water, are most convenient for use in practicing this method.

An alternative method of carrying out the method of the present invention involves the application of several coloring agents directly to the oxide surface to be multicolored where the agent is dissolved in a volatile solvent. Organic dyed materials such as Sandoz Acetasols Red 3BLS, Brown GLS, Blue RLS, etc.; Ciba Orocet Blue B, Scarlet BB, Yellow 2 RC; National Analine Oil Brown DV, Red 0, Blue BM, etc., may be dissolved at desired concentrations in organic solvents such as acetone, methyl-ethyl-ketone, and other oxygenated solvents. Depending upon the particular dyestuif, saturated or unsaturated, chlorinated organic solvents or aromatic solvents, as well as many other organic solvents, can be used to form solutions of concentrations which will impart an appropriate intense coloration to oxide coated metal. With reference particularly to an illustrative coloring agent, such as Ciba Oracet Blue B dye in solution in acetone, this dye may be applied to the anodized surface by painting to obtain desirable shading and artistic efiects. More intense coloration is obtained by use of repeated applications of the same color and this process may be combined as well with separate applications of different colors. In each case the solvent is removed rapidly due to its high volatility.

These solvent soluble dyes may be applied in combination with water soluble dyes such as Sandoz Red B through any conventional medium transfer technique such as stenciling, painting, spraying, brushing, etc. Further the water soluble materials may be employed using appropriate viscosity modifying agents such as the Waterthinned vehicles discussed above, and the water can then be removed by evaporation preparatory to the application of other coloring agents in water or other volatile solvent media.

After all the distinct coloring agents have been applied to the oxide surface and the excess solvents are removed therefrom, a protective coating is deposited in contact with the surface of the oxide to limit the removal or dispersal of the applied coloring agents due to leaching or other action of the sealing bath. The single protective coating is applied to all those areas containing colors and may be conveniently applied to the entire surface of the anodized sheet. After the protective coating is formed on the oxide surface, the sealing operation can be carried out without causing a significant change in the array of coloring agents as applied to the oxide, or a loss of definition of edges of the individual colored areas.

It will be appreciated that the foregoing steps and processes can be employed in combination with previously known and used operations for imparting a plurality of colors to metal surfaces.

For example, the water insoluble protective polymeric overlayer may itself contain coloring agents and these coloring agents can be imparted to the anodized film at the time of the sealing of the film along with other coloring advantages present in contact therewith.

Alternatively, where several areas of the anodized film are colored and protected with an overlayer of a polymeric coating material insoluble in water but permeable to moisture, the areas free of such organic resists may be colored by immersion of the entire surface into an aqueous dye bath dye, heated to a temperature of 70 C. or above.

Similarly, other known techniques appearing in the patent and technical literature may be used in combinations with the above techniques and processes.

Since many examples of the foregoing procedures may be carried out and since many modifications can be made therein without departing from the scope of the subject invention, the foregoing is to be interpreted as illustrative only and not as defining or limiting the scope of the inventions.

What is claimed is the following:

1. The method of applying multicolor arrays to anodized sheet which comprises: providing an unsealed anodized aluminum sheet; disposing a first layer of a waterthinned, water dispersible vehicle containing a water soluble coloring agent in intimate, contacting relationship with said sheet; drying said first layer; placing a second layer of an adherent, protective coating material permeable to moisture but resistant to being thinned by water in intimate, contacting relationship with said dried first layer; drying said second layer; sealing by immersion in hot water; and removing said protective coating material and said water dispersible vehicle.

2. The method of applying multicolor arrays to anodized sheet which comprises: providing an unsealed anodized aluminum sheet; disposing a first layer of a waterthinned, water dispersible vehicle containing a water soluble coloring agent in intimate, contacting relationship with said sheet; drying said first layer; placing a second layer of an adherent, protective coating material permeable to moisture but resistantto being thinned by water in intimate, contacting relationship with said dried first layer; drying said second layer; sealing by immersion in hot water; and removing said protective coating material and said water dispersible vehicle.

3. The method according to claim 1 wherein said vehicle is selected from the group consisting of gelatin, glue, casein, starches, polyvinyl alcohol and gum tragacanth.

4. The method according to claim 1 wherein said protective coating is a resin selected from the group consisting of acrylic, nitrocellulosic, vinyl and acetic based resins.

References Cited by the Examiner UNITED STATES PATENTS 2,510,857 6/1950 Bihlrnan 29527 2,778,790 1/1957 Sobol.

2,799,081 7/1957 Farnham 29--195 2,897,588 8/1959 Chapman 29527 2,906,009 9/1959 Knoll 29195 3,079,309 2/ 1963 Wainer.

JOHN H. MACK, Primary Examiner.

HYLAND BIZOT, MURRAY TILLMAN, WINSTON A. DOUGLAS, Examiners. 

1. THE METHOD OF APPLYING MULTICOLOR ARRAYS TO ANODIZED SHEET WHICH COMPRISES: PROVIDING AN UNSEALED ANODIZED ALUMINUM SHEET: DISPOSING A FIRST LAYER OF A WATERTHINNED, WATER DISPERSIBLE VEHICLE CONTAINING A WATER SOLUBLE COLORING AGENT IN INTIMATE, CONTACTING RELATIONSHIP WITH SAID SHEET, DRYING SAID FIRST LAYER; PLACING A SECOND LAYER OF AN ADHERENT, PROTECTIVE COATING MATERIAL PERMEABLE TO MOISTURE BUT RESISTANT TO BEING THINNED BY WATER IN INTIMATE, CONTACTING RELATIONSHIP WITH SAID DRIED FIRST LAYER; DRYING SAID SECOND LAYER; SEALING BY IMMERSION IN HOT WATER; AND REMOVING SAID PROTECTIVE COATING MATERIAL AND SAID WATER DISPERSIBLE VEHICLE. 